1. Field of the Invention
The present invention relates to an actuator that can drive a movable rod using fluid pressure or electric power.
2. Related Art
Japanese Patent Publication No. JP-A-11-272332 discloses a positioning cylinder device. The cylinder device has a ball screw and a nut that are disposed in a piston rod of a cylinder. In this configuration, a linear motion of the piston is converted into a rotation motion through the ball screw, and the rotation motion is converted into a positional signal by an angle sensor (for example, an encoder). Then, a switch valve is fed back on the basis of the signal, and the piston is positioned.
In JP-A-11-272332, with this configuration, a position of a stroke end of the piston rod can be changed. Further, in JP-A-11-272332, there is disclosed a case where the piston rod is driven by a motor as well as an electro-hydraulic servo valve.
However, according to the configuration of FIG. 1 of JP-A-11-272332, when an oil pressure is lost, it may be impossible to drive the piston, and thus redundancy enough to use as an actuator for driving a control surface of an aircraft may be not secured. Similarly, according to the configuration of FIG. 3 in JP-A-11-272332, if a voltage is lost, it may be impossible to drive the piston earliest.